It is known to use flexible or rigid endoscopes for surgery in narrow and deep cavities of the body. In most cases, the viewing channels are defined by image conductors. The transmission of images via image conductors has, however, serious disadvantages with respect to color quality and the resolution obtained. These disadvantages are avoided in rigid endoscopes.
Precise surgical work often requires a spatial image impression. Rigid endoscope configurations are known having different structural lengths and diameters as are stereoscopic systems. In this connection, reference may be made to published German patent application 1,766,803, German utility model registration 1,996,605 and U.S. Pat. No. 4,061,135. These known systems have an elongated base body in which two parallel sets of optics are arranged for stereoscopic viewing or photography. The use of separate optics for the stereo component beam paths leads, however, in several embodiments together with the instrument and viewing channel to a total tube diameter in the range of 25 to 30 mm which greatly limits the area of application of such endoscopes.
The two viewing channels must be adjusted with respect to each other in a complex manner for good stereoscopic imaging; more specifically:
a) with respect to the image position, with the position of the two images being different because of the given refractive index tolerance, thickness tolerance and radii tolerance and only being permitted to vary within narrow limits; and, PA1 b) with respect to the binocular error, with the optical axes of both viewing channels being strictly aligned parallel to each other with a deviation of a few angular minutes.
The required adjustment in such systems would have to be made ideally within the endoscope tube which however can hardly be done because the endoscope tube is not easily accessible for manipulation.
For a rigid endoscope, U.S. Pat. No. 4,364,629 discloses utilizing a rod-shaped accessory objective in a surgical microscope in lieu of the main objective having a long focal length. In this known solution, the large stereo basis of the surgical microscope is adapted to the stereo basis of the accessory objective with a prism system. The stereo basis of the accessory objective is less by approximately a factor of ten. A disadvantage of this known solution is that the stereo angle and therefore also the stereo impression is reduced by the same factor of ten. For practical applications, such as for laparoscopy, the largest possible objective field diameters are required which perforce reduces the stereo angle still further as will be made clear in the disclosure which follows. For this reason, the actual task of stereoscopic imaging cannot be satisfactorily solved with this known suggestion.
A further disadvantage of the known solution is that the large diameters of the two stereo beam paths of the surgical microscope (apparatus pupils) of approximately 16 mm are adapted with the prism system alone to the stereo beam paths of the accessory objective with the stereo beam paths, in turn, being less in diameter by approximately the factor 10. This causes unacceptably intense vignetting to occur with all generally known disadvantages for tile imaging characteristics. An amplification of the vignetting effect occurs also because the apparatus pupils of the surgical microscope are not identical to the exit pupils of the attachment objective.
U.S. Pat. No. 5,122,650 discloses a solution for an optical system for displaying three-dimensional endoscopic images. This solution provides that the object is imaged with a main objective at infinity and that for the two stereoscopic imaging beam paths respective imaging optics are provided rearward of the main objective for generating two mutually adjacent stereo component images as intermediate images in the finite range. These intermediate images are either imaged on two CCD chips or are transmitted via video electronics onto a monitor and are viewed with special spectacles or the intermediate images are transmitted via a rod-shaped optic into a viewing plane for viewing. A disadvantage of this solution is that a large diameter for the optical system is required because of the imaging of two mutually-adjacent stereo component images in one plane. A diameter of the optical system of at least 2b is necessary if it is intended to transmit an intermediate image of an object with the intermediate image having the magnitude b.
Published German patent application 4,116,810 discloses the use of a surgical microscope equipped with an endoscope. An endoscope is placed upstream of the surgical microscope such that a scissors-like joint piece is arranged between the main objective of the surgical microscope and the ocular of an endoscope. The joints are intended to be self-restraining so that they remain stationary in each image position in which they are placed by the physician. In this arrangement, neither data is given as to whether the endoscope even supplies a three-dimensional image having a satisfactory stereo basis nor how a stereoscopic image transmission from the endoscope to the surgical microscope should take place. Accordingly, doubt is present as to whether the surgeon receives a usable three-dimensional image by means of this arrangement.